we have a problem with one of our clients. The problem is related to a VM with 3 disks, 1 for the OS with 200GB and the other 2 for the data with 8TB and 13TB. Veeam 9.5 SP2 is installed on the host. The host is Windows Server 2012 R2 and the guest the same. It backups on a QNAP. No iscsi installed.The problem is that 9/10 the backup failes with these errors:

The shadow copies of volume \\?...67-11e7-80cf-00155d01a201} were aborted because volume \\?...67-11e7-80cf-00155d01a201}, which contains shadow copy storage for this shadow copy, was force dismounted.

A VSS writer has rejected an event with error 0x800423f4, The writer experienced a non-transient error. If the backup process is retried,the error is likely to reoccur.. Changes that the writer made to the writer components while handling the event will not be available to the requester. Check the event log for related events from the application hosting the VSS writer.

Support has ask me to open a call with Microsoft, because it seems there is a problem with the VSS. With Windows Backup if I do a Backup inside the VM it works correctly. If I start it from the host backing up only the VM affected with the problem, it fails like Veeam.